Demands for higher data rates for mobile services are steadily increasing. At the same time modern mobile communication systems as 3rd Generation systems (3G) and 4th Generation systems (4G) provide enhanced technologies, which enable higher spectral efficiencies and allow for higher data rates and cell capacities. As the demand for high-rate services grows faster than the cell capacities, operators are urged to increase the number of cells in their networks, i.e. the density of base stations increases. Base station transceivers are major contributors to the overall power consumption of a mobile communication network and therewith also major contributors to the OPerational EXpenditures (OPEX) operators are facing. One power saving strategy is to move processing capacity away from the base station transceivers and towards centralized processing units providing processing capabilities for several base station transceivers. The processing equipment of a base station transceiver consumes a significant part of a base station transceiver's total power, although the processing capabilities of a base station transceiver are only fully exploited in high load conditions, which do not occur permanently, but rather during peak hours only.
Currently, Radio Access Networks (RAN) use base stations or base station transceivers, as e.g. eNodeBs for the most recent technology Long Term Evolution (LTE) or LTE-A (LTE-Advanced), handling all radio, baseband and control functions. These base stations comprise voluminous antennas at elevated positions with electronic systems requiring considerable spatial installation volume. In addition, supplementary systems for power supply, air conditioning, etc. are to be installed in close proximity. In densely populated areas such installations are to be repeated over a grid of ˜1 km or less mesh width.
Mobile communication requires a highly specialized architecture of the RAN to interconnect the base stations efficiently with the telecommunication core network. Dedicated devices at strategic locations within the RAN perform functions like mobility anchoring, load balancing, paging (to find mobile devices not yet associated to a base station), and the like. Base stations offer the last hop within a RAN towards the mobile user (or the first hop in the flip or opposite direction) and relay the data forwarded from fixed network technology to radio technology. Due to the restrictions of the air interface of the underlying radio technologies, base stations have to be spread out in the area to ensure coverage and service continuity.
Recent developments on high speed optical and other fixed interfaces like the Common Public Radio Interface (CPRI) and the Open Radio equipment Interface (ORI) allow a separation of the radio part of a base station from the processing of the baseband. This leads to a decomposition of a base station transceiver into Remote Radio Head (RRH) and BaseBand Unit (BBU). Although this additional interface adds complexity to the RAN it offers a degree of freedom for placing the BBU.